Conventionally, micro-electromechanical system (MEMS) DC switches are relatively large in order to develop the large contact and return forces to provide a low resistance contact. These switches are often made from relatively massive gold cantilever or bridge structures having a large plate area for applying a force with an electric field from an actuation electrode from below. At the edge of the plate, one or more moving contacts, which necessarily can have a fairly high impact force when actuated into the fixed contact below, are located. There is usually a snap action to the actuation because of the physical effect of actuation where the force increases quadratically, whereas the cantilever spring return force increases linearly.
To mitigate these effects, significant interventions using extra electronics in the actuation circuit, for example, are often used to improve reliability and performance. Even with these interventions, there is a great tendency for the contacts to bounce, which is highly undesirable.
The bouncing induces other resonances in the structure, for example lateral vibrations because of insufficient lateral stiffness which can cause contact scraping. In addition, the large forces and impact tend to deform or otherwise move the contact metal on the contact surface with each actuation. The metal movement is necessary to achieve a large enough contact area and achieve a low contact resistance. This metal movement can also create micro-welds which are broken when the switch is opened. The moving of the metal of the contact is then an integral part of the switch achieving a low resistance since the surface is naturally too rough for intimate contact.
The contact pressure moves the metal to make the contact surfaces conformal and more intimate. When the contact opens, the breaking of the micro-welds will then cause the surface to roughen again. There may also be material transfer from one contact to another. This situation is not conducive to long term reliability.
However, by reducing the size, and therefore the mass of the micro-electromechanical system switch, changing the movement of the actuating cantilever, increasing the lateral stiffness, and improving the smoothness of the contact surface to atomic dimensions, the performance of a micro-electromechanical system switch can be greatly improved.
On the other hand, the MOSFET and other types of transistors have reached such high levels of development that the fundamental limits are beginning to block further development. The limits are related to semiconductors and insulator materials, which place limits in the ability to create thin barriers and high carrier densities.
The micro-electromechanical system switch approach allows the use of metals, having very high carrier densities, and actual modulatable physical gaps, which can have atomic dimensions. Even very small gaps of 2 nm between metal electrodes can have very large resistances. Reducing the gap to 0.5 nm can reduce the resistance many orders of magnitude. Therefore, one can achieve orders of magnitude larger transconductance with a micro-electromechanical system switch.
The conventional concept that micro-electromechanical system devices are too slow to compete with conventional transistors is mitigated when the distance moved is extremely small and the gain produced is extremely large.
Therefore, it is desirable to provide a micro-electromechanical system switch having electrodes that never come into intimate contact, but maintain a separation; for example, a separation of at least 0.5 nm. This separation allows the switch to operate as a contactless switch, thereby avoiding stiction or wear issues.
However, as noted above, one of the major issues with contacts in micro-electromechanical system switches is that the surfaces of the contacts tend to accumulate water and hydrocarbons. Not only is this an issue for all micro-electromechanical system switch designs, but when making a micro-electromechanical system having the desired contactless feature described above, the accumulation of water and hydrocarbons on the surfaces of the contacts is a particularly serious problem since it will only take a couple of mono layers before the gap is totally filled in the closed position and the device may no longer switch. In addition, the small gap of such a micro-electromechanical system switch has an especially large attraction for molecules.
Therefore, it is further desirable to provide a micro-electromechanical system switch having electrodes that never come into intimate contact in an environment which essentially prevents the accumulation of water and hydrocarbons in the separation gap.